Bring a medium pot of water to a boil. Place the green beans in boiling water and cook for 3 minutes. Drain and run under cold water for 1 minute.
Heat 1 Tbsp. oil in a large skillet, add garlic slices and cook until golden brown and crispy. Remove garlic from the hot pan and add sliced mushrooms. Sauté mushroom over medium-high flame for about 7 minutes, until they begin to brown and turn crispy. Add more oil if needed. Season with salt and pepper, to taste. Remove mushrooms from pan and set aside. Add another Tbsp. of oil to the pan along with blanched string beans. Sauté for 5 minutes. Plate green beans and top with crispy mushrooms, garlic and minced scallions.